The present invention relates generally to fastening systems. In particular, the present invention relates to a screw for penetrating and securing a workpiece.
In construction and furniture building involving wood products, the use of alternative materials is becoming more common. Some alternative materials are made entirely from post-consumer polyethylene waste such as bottles and other recycled plastics. Other alternative materials are manufactured by mixing wood and other materials such as glass, steel, and carbon fibers with a suitable binder to vary the characteristics of the final material. Materials alternative to wood are used to construct everything from cabinets to decks. Such alternative materials are made by various processes. For example, alternative material lumber may be made by blending recycled plastic resins with sawdust and extruding the blended mixture into standard lumber sections.
Such alternative materials have many advantages over wood. The alternative materials are often stronger and more durable then even pressure treated lumber. Many materials also offer better resistance to moisture, corrosive substances, termites and other insects, and other environmental strains that often prove to be detrimental to wood.
The use of standard fasteners with these alternative materials, however, may produce unwanted results. Screws are commonly used to affix one workpiece to another. However, some of the above mentioned alternative materials may not compress as readily as wood to accommodate the added volume of the inserted screw. With respect to some of the above-mentioned alternative materials, insertion of the screw, particularly if there is no pre-drilled hole to accommodate the screw, can cause remnants or shavings to be cut, extruded, or otherwise removed from the hole made by the screw. Such alternative materials may be referred to as xe2x80x9cremnant-producingxe2x80x9d materials, and may include materials in addition to the alternative materials mentioned above. Some of the remnants may remain attached to the material or held to the material by the screw, and extend above the material surface. These remnants then have to be removed by sanding or other methods. A common way to reduce this problem is to pre drill holes in the locations where a screw-type fastener must be inserted. This technique is laborious and time consuming. What is needed is a fastener adapted for use with a remnant-producing material where insertion of the fastener, particularly without pre-drilling holes, leaves a smoother surface on the remnant-producing material, reducing or eliminating remnants.
The present inventions provide a fastener for securing remnant-producing materials, a method of manufacturing the fastener, and a method of using the fastener so that remnants or slivers produced by rotation of the fastener are substantially embedded within the remnant-producing material.
A fastener is provided having two separate threaded portions, a first or lower threaded portion having a first thread pitch and a second or upper threaded portion having a second thread pitch. The leading lower thread portion is designed to engage the work piece more firmly than the following upper thread portion. Thus, upon insertion of the screw, as both threaded portions engage the work piece, the first section substantially maintains its position or insertion rate with respect to the work piece defined by the pitch of the lower threads. The second threaded portion having a different thread pitch engages the work piece less firmly and thus is pulled through the work piece by the first set of threads substantially at the rate defined by the angle of the first set of threads. If the respective upper and lower thread pitches were equal, the upper threads would merely follow in the tracks or parallel to the tracks of the first leading threads. By making the thread pitches different, the second threaded portion engages and pulls with it remnants and/or wall material, retaining or pulling it into the bore.
In one aspect of the present inventions, the pitch of the second portion threads is less than the pitch of the threads of the first portion. The second threaded portion pitch in such an embodiment may spiral in the same direction as the first thread portion, may be of zero pitch, i.e., one or more rings around the screw shank, or may be of negative pitch, i.e., spiral in a direction that is opposite of the threads on the first or lower threaded portion.
In another aspect of the present inventions, the threads on the second or upper threaded portion have a larger diameter than the threads on the first or lower threaded portion.
In use, the first or lower threaded portion of the fastener is engaged with the remnant-producing material and rotated in the direction of the threads to insert the fastener into the material. This rotation may produce remnants or slivers by extruding, cutting, or some other mechanism. These remnants may extend from the hole in the material or workpiece surface made by the screw.
After the lower threaded portion is completely inserted into the material, the upper threaded portion of the fastener enters the material. Because the upper threaded portion has threads that have a different thread pitch relative to the threads on the lower threaded portion, the threads on the upper threaded portion capture the remnants that have been extruded within and/or onto the surface of the workpiece. As the fastener is completely inserted into the material, the remnants that have been extruded by the lower threaded portion of the fastener are substantially retained in the bore by the upper threaded portion of the fastener.
Therefore, a fastener and a method for inserting the fastener are provided to answer a need that currently exists in the construction industry.
These and other features and advantages of the invention will be more clearly understood from the following detailed description and drawings of preferred embodiments of the present invention.